Method of manufacturing film carrier type substrate

ABSTRACT

A film carrier type substrate includes a film made of organic high molecular substance, a metal layer formed over the film by depositing metal vapor and irradiating nitrogen gas ions on the film and a mixing layer made of a mixture of the materials of both the metal layer and the film formed in the interface between the metal layer and the film. Prior to forming the metal layer, inert gas ions and/or nitrogen gas ions may be irradiated on the film in advance.

BACKGROUND OF THE INVENTION

The present invention relates to a film carrier type substrate used, forexample, for high density mounting of integrated circuits, which isbased on the film carrier system, and to a method of manufacturing thefilm carrier type substrate.

The film carrier system among (IC) integrated circuits mountingtechniques has attracted a special attention because of its advantageousfeatures of a continuous IC mounting process and high bonding speed.

The film carrier type substrate used for the film carrier system isconventionally categorized into two types of substrates. (1) The firsttype of substrate is shown in FIG. 1. As shown, a copper foil 13 isbonded onto a film 11 by means of adhesion 12. The copper foil 13 thusbonded is etched to form a pattern of a desired electric circuit. (2) Inthe second type of substrate, an electric pattern made of copper, nickelor the like is formed on the surface of the film 11 by non-electrolyticplating process. In either type of substrate, the film 11 is made of anorganic high molecular substance, mainly polyimide.

The substrate with a copper foil bonded thereto, involves the followingdisadvantages. (1) Since the adhesion layer 12 is interlayered betweenthe film 11 and copper foil 13, poor thermal conductivity is presentbetween them. (2) The adhesiveness between the film 11 of polyimide orthe like and the copper foil 13 is unsatisfactory. (3) When the filmcarrier type substrate undergoes temperature of 150° or more for a longtime, the bonding of the film 11 and the copper foil 13 is remarkablydeteriorated.

The substrate formed by the non-electrolytic plating process as wetprocess is disadvantageous in that (1) adhesion properties of theplating layer is not uniform, and (2) a strict management is requiredfor plating solution to avoid environmental pollution.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a filmcarrier type substrate which succeeds in solving the problems of theconventional one, and a method of manufacturing the same.

A film carrier type substrate of the present invention comprises a filmmade of organic high molecular substance, a metal layer formed over thefilm, and a mixing layer formed in the interface of the film and themetal layer, the mixing layer made of a mixture of the materials of boththe film and the metal layer.

In a first method of manufacturing a film carrier type substrateaccording to a first aspect of the present invention, in vacuum, metalvapor is deposited on a film made of organic high molecular substanceand accelerated nitrogen gas ions are irradiated on the film, whereby ametal layer is formed over the film and a mixing layer made of a mixtureof the materials of both the metal layer and the film is formed in theinterface between the metal layer and the film.

In a second method of manufacturing a film carrier type substrateaccording to a second aspect of the present invention, in vacuum, inertgas ions and/or nitrogen gas ions are irradiated on a film made oforganic high molecular substance. Then, metal vapor is deposited on thefilm, and accelerated inert gas ions and/or accelerated nitrogen gasions are irradiated on the film. Consequently, a metal layer is formedover the film and a mixing layer made of a mixture of the materials ofboth the metal layer and the film is formed in the interface between themetal layer and the film.

The film carrier type substrate of the invention, as a metal layer isformed over a film made of organic high molecular substance, issatisfactorily flexible. Further, since the mixing layer functions likea coupling member, an adhesive force of the metal layer to the film isstrong. Accordingly, the metal layer hardly peels off the film. Further,the thermal conduction between the film and the metal layer is goodsince no adhesive is placed between the film and the metal layer.

When the first manufacturing method of the invention is used, the filmcarrier type substrate can be manufactured by dry process in an easy andlow-cost manner. The quality of the resultant products is uniform.Further, the control of the thickness of the metal layer and the mixinglayer is easy, and the patterning of the metal layer is easy.

When the second manufacturing method of the invention is used, the sameeffects as those obtained in the first method are obtained. Further, thefirst film surface exposure to the gas ions forms an amorphous carbonlayer on the film surface, and sputters subsurface oxygen on the filmsurface, which is supposed to cause the adhesiveness of the mixing layerto be reduced when environment (here, time elapse, heat cycle, etc.)changes or when the substrate is immersed in etching solution ofhydrochloride acid series. That is, the surface exposure to the gas ionsremarkably reduces the amount of oxygen on the film surface.Accordingly, the mixing layer formed on the film surface contains a lessamount of oxygen, and the metal layer is intimately layered on themixing layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, partial cross sectional view showing aconventional film carrier type substrate,

FIG. 2 is an enlarged, partial cross sectional view showing a filmcarrier type substrate according to the present invention,

FIG. 3 is a schematic diagram showing an apparatus for executing themethod of manufacturing a film carrier type substrate according to thepresent invention, and

FIG. 4 is a schematic diagram showing a modification of an apparatus forexecuting the method of manufacturing a film carrier type substrateaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 2 is an enlarged, partial cross sectional view showing an exampleof a film carrier type substrate according to the present invention. Inthe film carrier type substrate 20, a metal layer 23 of high electricconductivity, which is made of any of materials such as Au, Ag, Cu, Ni,and Al, is formed on a film 21 made of organic high molecular substance,for example, polyimide. A mixing layer 22 is formed in the interface ofthe film 21 and the metal layer 23. The mixing layer is made of amixture of the materials of both the film and the metal layer, i.e.,organic high molecular substance and the metal.

The metal layer 23 may be formed over the entire surface of the film 21or may be formed on the surface of the film 21 in the form of anelectric circuit pattern.

The thickness of the metal layer 23 is preferably within the range of0.1 μm to 50 μm. Selection of the thickness range is based on the factsthat the thickness of less than 0.1 μm will provide insufficientelectric conductivity, and the thickness of more than 50 μm will providepoor flexibility of the film 21 and increase the cost to manufacture.

The thickness of the mixing layer 22 is preferably within the range ofapproximately 5 nm to 500 nm. The thickness of such a range will providesatisfactory adhesion properties. When the thickness is selected to bein excess of the upper value of the range, the film 21 will lose itsflexibility.

The features of the film carrier type substrate 20 thus constructed arelisted below.

(1) The flexibility of the substrate is satisfactory, or at leastequivalent to that of the previously described substrate. This is due tothe fact that the metal layer 23 is adhesively formed on the film 21made of organic high molecular substance.

(2) Since the mixing layer 22 functions like a coupling member, theadhesiveness of the metal layer 23 to the film 21 is high. Accordingly,the metal layer highly resists peeling off the film.

(3) No adhesion is present between the film 21 and the metal layer 23,and the compositions continuously vary in the interface between the film21 and the metal layer 23 due to the mixing layer 22. Therefore, thermalconductivity is excellent between the film 21 and the metal layer 23.

A first method of manufacturing the film carrier type substrate 20according to the present invention will be described with reference toFIG. 3. FIG. 3 is a schematic view showing an example of an apparatusfor executing the substrate manufacturing method of the invention.

A film 21 as described before is mounted on a holder 30 and is placed ina vacuum chamber (not shown). A vapor source 32 and an ion source 38 aredisposed to be directed toward the film 21. The vapor source 32, such asan electron beam vapor source, heats metallic material 34 to evaporateit, and deposits metal vapor 36 on the film 21. The ion source 38,preferably a bucket type ion source, ionizes nitrogen gas G suppliedthereinto and accelerates nitrogen ions, which are distributed uniformlyover a large area, toward the film 21. The ion source is capable ofprocessing a large area at one time. Reference numeral 42 designates afilm thickness monitor for monitoring the thickness of a thin filmformed over the film 21.

The metal vapor 36 may be vapor of any of high electrical conductivity,such as Au, Ag, Cu, Ni, and Al.

In the process of manufacturing the film carrier type substrate, thevacuum chamber is evacuated up to approximately 10⁻⁵ to 10⁻⁷ Torr.Subsequently, metal vapor 36 from the vapor source 32 is deposited onthe film 21, and, at the same time or alternately, accelerated nitrogengas ions 40 supplied from the ion source 38 are irradiated toward thefilm 21. At this time, if required, cooling medium such as cooling watermay be supplied to the holder 30 thereby to cool the film 21.

A plurality of vapor sources 32 and a plurality of ion sources 38 may beused when the area of the film 21 to be processed is large.

Through the above process, the metal layer 23 as described above isformed on a film 21. Further, through the knock-on action of the ions40, the mixing layer 22 as described above is formed in the interface ofthe film 21 and the metal layer 23. As a result, the film carrier typesubstrate 20 as shown in FIG. 2 is manufactured.

The metal layer 23 can be easily adjusted to a desired thickness, forexample, 0.1 μm to 50 μm, by using the film thick monitor 42, forexample.

The thickness of the mixing layer 22 depends on the acceleration energy(or average projection distance) of the ions 40 and a dosage of theirradiated ions. An excessive thickness of the mixing layer 22(resulting from excessive increase of acceleration energy of ions 40and/or dosage of irradiated ions) will create some problems. Forexample, as the substrate is deteriorated with irradiation of ions, thefilm loses its flexibility, and the cost of the apparatus is increased.Also, the thickness of the mixing layer 23 between 5 nm and 500 nm issufficient in view of adhesion of the mixing layer 23. Accordingly, theacceleration energy of ions 40 is approximately between 500 eV and 10KeV, preferably 20 KeV or less. The dosage of irradiated ions areselected to be within the range from 1.0×10¹⁴ to 1.0×10¹⁸ ions/cm².

The vapor deposition and ion irradiation may be carried out through amask with a predetermined pattern. If done in this manner, a patternedmetal layer 23 as an electric circuit is formed on the film 21 withoutany additional step. Alternately, an electric circuit pattern may beformed in a manner that the metal layer 23 is formed over the film 21 asin the previous manner, and then the formed metal layer is etched toform a desired electric circuit pattern by conventional etching process.

Following are advantageous features of the substrate manufacturingmethod of the invention:

(1) The film carrier type substrate 20 having features as stated abovecan be manufactured by dry process and in easy and inexpensive manner.The products manufactured have uniform product quality.

(2) Adjustment of the thickness of the metal layer 23 and the mixinglayer 22 is easy. Accordingly, it is easy to manufacture the filmcarrier type substrate 20 with excellent characteristics in accordancewith required usage.

(3) The substrate surface has good smoothness. The resultant filmcarrier type substrate 20 exhibits good adhesive properties against ICchips, for example, and good thermal conductivity.

(4) The metal layer 23 may be patterned in the process of forming themetal layer, without any additional patterning process.

EXAMPLE 1

An apparatus as shown in FIG. 3 was used. Cooling water was fed to theholder 30. A polyimide film of 0.15 mm thick was set to the holder 30.Metallic evaporated material 34 of the vapor source 32 was oxygen-freecopper. It was heated with electron beams to evaporate. Vapor ofoxygen-free copper was deposited over the film. At the same time,nitrogen gas ions from the ion source 38 was accelerated with the energyof 5 KeV and was irradiated on the film. At this time, the currentdensity on the holder 30 was 16.7 μA/cm². The rate of evaporating copperwas 5.0 Å/sec. The process was continued for 100 seconds. A film carriertype substrate as stated above was manufactured.

A peeling test was conducted for evaluating an interface strength of thepolyimide film and the copper deposited film thus formed. The results ofthe evaluation are shown in Table 1.

The evaluations of the substrate which experienced only the vacuumdeposition, that is, did not experience the ion irradiation, and thesubstrate which underwent the IVD (Ion Vapor Deposition) process usingAr gas ions under the conditions similar to those of the case usingnitrogen gas ions are additionally shown in the table, for comparison.As seen from the table, irradiation of nitrogen gas ions remarkablyimproves the adhesive properties, so that the films were broken whilethe copper layers were left sticking to the film and measurement couldnot be carried out.

                  TABLE 1    ______________________________________            Not treated                    Ar ions (IVD) N ions (IVD)    ______________________________________    Peel strength              0.2 (kg/cm)                        1.2 (kg/cm)   Film broken    ______________________________________

A second method of manufacturing the film carrier type substrate 20according to the present invention will be described with reference toFIG. 4. FIG. 4 is a schematic view showing an example of an apparatusfor executing the substrate manufacturing method of the invention whichhas the same construction as the apparatus shown in FIG. 3 except forthe inclination θ of an ion source 38. The second method issubstantially the same as the first method described before except thatinert gas ions and/or nitrogen gas ions are irradiated on a film oforganic high molecular substance in advance.

In the process of manufacturing the film carrier type substrate, thevacuum chamber is evacuated up to approximately 10⁻⁵ to 10⁻⁷ Torr.Subsequently, inert gas ions 40 are pulled out of the vapor source 38and is irradiated on the film 21. The inert gas ions 40 may be gas ionsof any of helium, neon, argon, krypton and the like. The acceleratingenergy of inert gas ions 40 is preferably 100 eV to 20 KeV. The dosageof inert gas ions is preferably 1.0×10¹⁴ /cm² or more. These valuesactually change depending on the kind of inert gas ions 40 and materialof the substrate 21. Accordingly, the most suitable values are selectedfor the respective factors. The ion incident angle θ may be within therange from 0° to 90°; however, 45° is preferable when taking theefficiency of sputtering into account. Thereafter, similarly to thefirst method according to the present invention, simultaneously oralternately with depositing metal vapor 36 on the film 21, theaccelerated nitrogen gas ions 40 supplied from the ion source 38 areirradiated toward the film 21. At this time, if required, cooling mediumsuch as cooling water may be supplied to the holder 30 thereby to coolthe film 21.

A plurality of vapor sources 32 and a plurality of ion sources 38 may beused when the area of a film 21 to be processed is large.

Through the above process, the metal layer 23 as described above isformed on the film 21. Further, through the knock-on action of the ions40, the mixing layer 22 as described above is formed in the interface ofthe film 21 and the metal layer 23. As a result, the film carrier typesubstrate 20 as shown in FIG. 2 is manufactured, which are substantiallythe same as the substrate obtained by the first method. Also, themanufacturing conditions, features etc. of the second method aresubstantially the same as those of the first method.

EXAMPLE 2

An apparatus as shown in FIG. 4 was used. Cooling water was fed to theholder 30. A polyimide film of 0.15 mm thick was set to the holder 30.Argon ions of 6.0×10¹⁶ /cm² were irradiated onto the film surface, withacceleration energy of 2 KeV. The incident angle θ of argon ions was 45°C. to the film surface. Metallic evaporated material 34 of the vaporsource 32 was oxygen-free copper. It was heated with electron beams toevaporate. Vapor of oxygen-free copper was deposited over the film. Atthe same time, argon gas ions from the ion source 38 was acceleratedwith the energy of 5 KeV and was irradiated on the film. At this time,the current density on the holder 30 was 16.7 μA/cm². The rate ofevaporating copper was 5.0 Å/sec. The process was continued for 100seconds. A film carrier type substrate as stated above was manufactured.

A peeling test was conducted for evaluating an interface strength of thepolyimide film and the copper deposited film of the substrate thusformed. In the test to peel the deposited copper layer from the film,all the films were broken while the copper layers were left sticking tothe film. For the flexibility of the films, no problem was found.

For comparison, the same test was conducted on the substrates in whichcopper was deposited on the film without any ion irradiation process.The copper deposited layer was easily peeled off the film. This wasconfirmed for all the substrates.

The results of the peeling test for the substrates one month afterformation of these substrates are shown in Table 2. The test result ofthe substrate in which the mixing film was formed on the film surfacewithout ion irradiation process in advance is contained in the table,for comparison.

As seen from the table, no deterioration of the adhesion properties withtime is observed for the substrate subjected to the ion irradiation inadvance.

                  TABLE 2    ______________________________________    No ion irradiation in                        Ion irradiation in    advance to film     advance to film    Immediate-              Immediate-    ly after     One month  ly after  One month    manufac-     after      manufac-  after    ture         manufacture                            ture      manufacture    ______________________________________    Peel   1.2       0.4        1.4     1.4    strength    (kg/cm)    ______________________________________

As described above, according to the present invention, a film carriertype substrate is sufficiently flexible, and has good adhesiveproperties of a metal layer against a film, and good thermalconductivity between the film and metal layer. Such an excellent filmcarrier type substrate can be manufactured by dry process and in easyand inexpensive manner. The resultant products are uniform in theproduct quality. The thickness adjustment of the metal layer and amixing layer is easy, and the patterning of the metal layer is alsoeasy. Further, especially according to the second method of the presentinvention, the adhesion properties of the mixing film is unsusceptive tothe etching solution of hydrochloride acid series, time elapse, heatcycle, and the like, since a less amount of oxygen is contained in themixing layer between the film and the metal layer.

What is claimed is:
 1. A method of manufacturing a film carrier typesubstrate in vacuum, comprising the steps of:depositing metal vapor on afile made of organic high molecular substance; and irradiatingaccelerated nitrogen gas ions on said film simultaneously with the stepof depositing metal vapor, an accelerating energy x of which is definedby the range 2 KeV<x<10 KeV, whereby a metal layer is formed over saidfilm and a mixing layer made of a mixture of materials of both saidmetal layer and said film is formed in an interface between said metallayer and said film.
 2. A method of manufacturing a film carrier typesubstrate in vacuum, comprising the steps of:irradiating acceleratedions of a gas selected from the group consisting of nitrogen and aninert gas on a film made of organic high molecular substance, wherein anaccelerating energy x of said ions is defined by the range 2 KeV<x<10KeV; and after the step of irradiating ions, conducting deposition ofmetal vapor on said film and irradiation of accelerated ions of said gason said film simultaneously, whereby a metal layer is formed over saidfilm and a mixing layer made of a mixture of materials of both saidmetal layer and said film is formed in an interface between said metallayer and said film.